Integral Projection Models and Sustainable Forest Management of Agave inaequidens in Western Mexico

Abstract

In México, at least 37 Agave species are extracted from wild populations for producing distilled spirits. This activity involves harvesting mature agaves just before producing their inflorescences, which cancels sexual reproduction of plants used. The increasing demand of agaves spirits in national and international markets is determining a strong pressure on wild populations, most of them lacking adequate management. In addition, the dynamics of agave populations may be affected by natural phenomena like oscillation of rainfall regimes, which affects the recruitment of agave seedlings, or the scarcity of pollinators that may affect seed production and general population dynamics. We studied the demography of wild populations of Agave inaequidens to analyze critical conditions for populations recovery, modelling the effects of rainfall trends on the demographic performance of this species, and exploring response of populations to hypothetical extraction regimes and reforestation efforts. Our study was performed in four well-conserved wild populations in Central Western Mexico, each population was sampled in a plot of about one hectare composed by 10 subplots 50 x 5 m (2500 m 2 ). Populations were monitored yearly between 2011 and 2013, measuring plant size, reproductive individuals, and fecundity. Data were analyzed through integral projection models by using the IPMpack for R, to perform prospective analyses. We in addition constructed stochastic models to explore the possible influence of rainfall variation on species demography, using data for the drier and wetter years of the study period. Population growth varied from λ=1.003 to λ=0.899 among populations and years, and exceptionally λ=0.559 after a fire event. Low rainfall decreases λ values, indicating especial limitations to harvesting agaves during dry years whose frequency most probably will increase. In general, extraction rates from 10% to 30% of mature individuals are viable to maintain λ above 1, and these rates may be higher if new plants are introduced in populations. Depending on levels of extraction, our models suggest that it is necessary to carry out actions of reforestation, and in situ management according to the trends found in each site. This is one indispensable condition to maintain λ close to or greater than 1. Sustainable extraction of wild agaves is possible, some communities are already carrying out a repertoire of goods practices in this direction, but together with ecological criteria and good management techniques, strict regulations and social organization are needed to achieve it.

Predicting the impacts of palm heart and fruit harvesting using Integral Projection Models

“…Some studies have shown that the evaluation of different harvesting techniques can help to improve them. These include harvesting time, season, frequency, a minimum size of individuals harvested, and artificial insertion of seedlings into the population (Ticktin, 2004;Endress et al, 2006;Torres-García et al, 2020). Freckleton et al (2003) simulated E. edulis harvesting during the pre-reproductive and postreproductive seasons and found that the populations tolerated higher levels of palm heart harvesting if it was conducted after the reproductive period, not previously.…”

“…Different management methods have been evaluated, including harvesting time, intensity, frequency, life form, and plant part harvested (Ticktin et al, 2002;Endress et al, 2006;Vallejo et al, 2014). As the harvesting of herbs commonly leads to mortality, influences on demographic parameters are negative and stronger (see Ghimire et al, 2008;Torres-García et al, 2020), while leaf and fruit harvesting on palm and tree species, which do not cause the death of individuals tend to have weaker effects on population demography and be sustainable (see Zuidema and Boot, 2002;Zuidema et al, 2007;Sampaio et al, 2008). In general, harvesting has been shown to negatively affect vital rates and population growth rates (Schmidt et al, 2011).…”

A newly identified glycosyltransferase AsRCOM provides resistance to purple curl leaf disease in agave

“…Besides its use in producing natural fibers, A. H11648 could also be utilized for alcoholic beverages [ 2 ], nutraceuticals [ 3 ], and nanocellulose [ 4 ], making it a highly valuable crop. Despite its widely valuable usage, A. H11648 also faces a number of challenges due to its susceptibility to various biotic and abiotic stresses, such as cold temperatures [ 5 ], root rot disease [ 6 ], high temperatures [ 7 ], low rainfall [ 8 ], low aboveground biomass coverage [ 9 ] and agave purple curl leaf disease [ 10 ]. Among these various stresses, agave purple curl leaf disease poses a significant threat to the agave industry as it severely damages the plant’s leaves which are the primary source of its natural fibers and will cause a sharp reduction in leaves production by more than 30% in severe cases [ 11 ].…”